1. Field of the Invention
This invention relates to a MacPherson Strut assembly for wheel suspensions of motor vehicles, and more particularly to the area of elastic attachments for the MacPherson Strut assembly. Such attachments, in addition to being usable for wheel suspensions, can also be used for mounting engines, as well as for suspensions of stationary machines. More precisely, this invention includes the incorporation of hydraulic damping into the elastic connections of suspension attachments for the upper point of attachment of a shock absorber to a vehicle frame or chassis. In such MacPherson units, the shock absorber must also serve as the steering pivot. In addition, the invention also involves the application of a hydraulically damping suspension attachment as a so-called anti-torque link for the suspension of a power unit on a frame.
2. Background Information
The structure of automobile vehicle suspensions has become more and more standardized. The term "strut" is generally used for the unit carrying the helicoidal spring associated with a telescopic shock absorber. The ability of the shaft of this shock absorber to rotate provides the steering pivot in a front wheel drive vehicle which has MacPherson struts.
A MacPherson strut system is generally used on most subcompact and compact cars with front wheel drive. The MacPherson system features a long telescopic shock absorber strut surrounded by a coil spring. The upper end of the strut is generally isolated by a rubber vehicle mount that contains an oil-free ball bearing which allows for the turning of the wheel, while the lower end of the strut is typically attached to the steering knuckle of the lower control arm ball joint. The lower control arm can be attached to the underbody side apron of the vehicle, or to the lower side rails of the vehicle, and is also typically attached to the steering knuckle. A stabilizer bar can also be connected to both lower control arms and the front vehicle crossmember. It is also possible to have adjustable strut bars connecting the control arms to the subframe of the vehicle. This lower connecting and stabilizing structure in such a suspension system is typically referred to as the lower guide triangle.
Regardless of whether the lower guide triangle incorporates an anti-roll bar, the presence of a ball joint at the outer point of the guide triangle provides the possibility of simultaneous vertical deflection and pivoting of the shock absorber tube carrying the axle of the front wheel. The use of such a similar suspension can also be encountered in rear axle suspensions where either the microdeflections of a sophisticated triangulation, or the geometric configuration of a true steering layout for vehicles with four-wheel steering, are permitted by the existence of the ball joint.
Thus, the geometrical configuration of a front suspension, as well as that of a rear suspension, can be determined by the attachment of the upper end of a shock absorber shaft to the vehicle body. The shock absorber tube and the steering knuckle pivot are pivotable about the shaft in a manner guided by the triangle of the MacPherson system.
Under somewhat analogous conditions, an anti-torque link of an engine suspension can provide a reaction to engine forces in an essentially horizontal direction.
In known wheel suspensions of classic suspension systems, when a coil spring provides the vertical flexibility of the wheel suspension, the pivoting of the wheel suspension is permitted by a complementary support of a suspension cup, generally the upper cup, on a ball thrust bearing which transmits the permanent load to the vehicle body.
This complementary attachment requires, like the attachment of the shock absorber shaft concentric therewith, a filtering of vibrations to limit the vibrations transmitted through the spring. This function is generally provided by pieces of vulcanized rubber that are intimately connected to the cup and to a corresponding attachment sleeve.
The two concentric, elastic pieces which provide the limiting of vibration transmissions can complement each other to provide an improvement which constitutes the subject matter of numerous publications.
European Patent No. 0,249,369 to General Motors, for example, describes a device which exclusively improves the elastic connection between the shock absorber shaft and the chassis.
The device of European Patent No. 0,249,369 limits dynamic deformations by means of thrust washers, whereas the stresses of the vertical limit of travel on a shock absorber thrust bearing can be exerted by means of another rigid cup. The permanent load, in this case, is transmitted elsewhere in this arrangement.
Likewise, French Patent No. 2,583,126 to Honda describes a device which incorporate a roller thrust bearing for carrying the permanent load of the suspension spring. This device, however, only provides a good filtering of acoustic vibrations for the shock absorber shaft by means of a "vibration neutralizer".
In contrast, the device described in German Patent No. 3,034,743 to Continental combines, via a roller thrust bearing, in one complex piece, the permanent support of the suspension spring as well as the elastic ring where the connecting force is exerted in a dynamically alternating manner between the shock absorber shaft and the support on the body. More particularly, this German patent is basically directed to the environment of the ball thrust bearing. Because of this design, the stresses of the dynamic limit of travel are exerted on the attachment of the shock absorber shaft due to the presence of a rubber thrust bearing. The stresses are not transmitted through the ball bearing, which carries a low-variation load, since the low-variation load is modulated exclusively by the flexibility of the spring, even in the case of rapid deflections.
In an analogous manner, French Patent No. 2,563,302 to AB Volvo describes a device called a suspension strut mount in which a small space in the mount permits a short, free displacement between thrust bearings in the interior of the upper attachment of the shock absorber shaft, which attachment also carries the permanent load of the spring.
Improvements which introduce hydraulic damping into the upper attachment point of a shock absorber of a MacPherson tube generally rely on the attachment of the shock absorber shaft which receive the stress from the dynamic thrust at the vertical limit of travel as a consequence of the impact of the shock absorber tube impinging upon an elastomer thrust bearing.
This method of improving the vibratory comfort of a vehicle, by reducing the vibrations caused by stresses from the wheel, is described in French Patent Nos. 2,587,774 and 2,623,866 to Tokai Rubber. Such improvements may also apply exclusively to the connection of the shock absorber shaft to the body, or to analogous applications, without any concern as to the carrying of the permanent load by the suspension spring. These devices consist of a single piece having two opposite chambers connected together by a liquid conduit, the liquid conduit being wound about the outer diameter of the chambers. This conduit exhibits a great length and a considerable cross section. These devices, whose effects of inertia block any deformation if the shock absorber exerts rapid stresses, nevertheless permit deflections during slower movements due to guidance, either by means of a ring concentric with the attachment, whose elastomer material is pre-stressed in order to improve the resistance to fatigue, as in French Patent No. 2,587,774, or by means of an annular part with radial deflection, as in French Patent No. 2,623,866. Nevertheless, these deflections are generally limited by the integration of elastomer thrust bearings into the hydraulic chambers.
In another application, French Patent No. 2,356,847 to Automobiles Peugeot, describes an improved shock absorber device, having two chambers separated by a rigid partition. This rigid partition can be associated with an anti-torque link in order to provide reaction to engine torque as a complement of the suspension.
The design of such attachment devices can be very complex in order to provide the sole, very limited function of a point of elastic attachment. The fulfillment of the other described functions, such as the maintenance of a permanent force, requires a similar degree of complexity in order to provide the consistency of the level of quality demanded from the acoustic or vibratory filtering of the connections between an automobile chassis and a wheel or power unit suspension.
An analysis of the known devices shows that none of them meet all of these functions in a satisfactory, and simplistic manner. In other words, none of the known devices meet the requirement of transmitting a permanent load in all directions while still efficiently isolating the elastic connection from acoustic frequencies.